(1) Field of the Invention
The present invention relates to packet forwarding apparatus and, more particularly, to a packet forwarding apparatus equipped with redundant routing control information processing modules capable of switching their operation modes.
(2) Description of the Related Art
In recent years, as the Internet has come into popular use while fields of application of IP networks have expanded, high reliability is required for IP networks provided by carriers. On IP switching nodes (routers) that forward packets carried over one line onto another line at connection points on the Internet, a huge amount of routing information covering several tens of thousands of routes across the Internet is retained. Each router exchanges routing control packets with the other routers on a network, using a specific routing protocol, and updates the routing information retained on it. Each router is required to have a function of forwarding packets at a high speed and its data throughput is reaching into terabits per second.
Therefore, when a failure occurs in a packet forwarding processor of one router, quite a huge amount of communication data will be lost per unit time. In the case where a failure should occur in a routing controller of a router, packet forwarding onto an incorrect route might take place until a new alternative route is set up on the network by a function of the routing protocol used. For these reasons, an IP router adopting a redundant system configuration is proposed. This type of IP router is equipped with multiple routing protocol processing modules which are generally called routing modules, one of which operates as active one with the remaining being standby. The standby routing module is activated upon a failure of the active routing module to take over the routing protocol processing. Such a configuration having redundant routing protocol processing modules can significantly reduce the time from the failure occurrence to recover, as compared with a configuration where the failed module is manually replaced by a new module.
According to the redundant system configuration in which the standby routing module is activated upon the failure of the active routing module, however, a considerable time is taken before the recovery to the normal state of the routing control function because the module that has become active by operation mode switching has to collect routing control information from other routers, existing in its vicinity and operating with the same routing protocol, and reconfigure a new routing table.
To solve the above problem, for instance, Fujitsu, Ltd. proposed an IP switching node in which multiple redundant routing modules (hereinafter referred to as routing control modules) are always operating and the routing control information held by a standby routing control module keeps consistent with that information held by an active routing module, as described in a Fujitsu publication entitled “GeoStream R900 Series Product Report Vol. 1 (High Reliability Part)” ([online], November, 2001, Internet, URL:http://telecom.fujitsu.com/jp/products/report/geostream_r900/report_r900.pdf (Non-patent document 1).
According to the above prior art system, upon occurring a failure in the active routing control module, the standby routing control module can start operation as the active one because it is already activated. In this case, since the standby routing module is already run and has a database of routing control information prepared already, it can take over the routing protocol processing, in principle, without collecting routing control information from other node apparatuses. For the packet forwarding apparatus described in Non-patent document 1, routing control information that is held by the standby routing control module is updated in different ways according to types of routing protocols, as will be described below.
In the case of a Routing Information Protocol (RIP) which is a distance vector type routing protocol, routing control information received from another node apparatus on the network is notified to both the active and standby routing control modules and each module reconfigures or updates its routing information database independently of each other.
In the case of an Open Shortest Path First (OSPF) which is a link state type routing protocol, routing control information received from another node apparatus is notified to the active routing control module and the database information reconfigured on the active routing module is reflected (copied) to the database on the standby routing module by communication between the active and standby routing modules.
In the case of a Border Gateway Protocol (BGP) which is a path vector type routing protocol, the active and standby routing control modules respectively set up separate TCP connections to a peer router and both modules receive routing control information from the peer router and reconfigure or update their routing information databases independently of each other.
Therefore, for the packet forwarding apparatus described in non-patent document 1, if the applied routing protocol is OSPF, routing information updated on the active routing module has to be copied to the standby routing module. This increases the amount of data to be communicated between the modules and each of routing control modules is required to have a high-speed information processing function.
For the above apparatus, if the applied protocol is OSPF or BGP, both the active and standby routing modules update their own routing information databases, but information about the database update state is not communicated between these modules. In the above prior art, the active routing module periodically monitors the standby routing module to prevent an unsuccessful failover in case of the standby routing module malfunction. However, in the case of OSPF or BGP, it cannot be guaranteed that the routing information databases on the active and standby routing modules are actually consistent with each other.